This invention relates to a driving device with a protection circuit for driving a light emitting element via a low operating voltage, especially to the protection circuit utilizing three transistors to protect the driving device.
Because the properties such as long life, low operating voltage needed, fast response, good shock tolerance are needed to fit the requirements of products for being light, thin and miniature, the light-emitting element like light-emitting diodes, laser diodes and liquid crystal diodes not only are applied popularly in the business but also speed up the vigorous developments of the photoelectric industries.
In view of the above-mentioned, some kinds of devices for driving the light-emitting element via a relative low power voltage have been proposed and these devices usually have more transistors or complex circuits composed of some integrated circuit devices.
Some light-emitting elements operated near or above 3V need a protection circuit to, maintain normal operation and protect the light-emitting elements. Therefor, how to drive the light-emitting element by the least operating voltage and ensure that it works normally and makes the best economical benefits is the major consideration of this invention. For example, FIGS. 1(a)xcx9c(c) show that conventional protection devices for driving the light-emitting element via an operating voltage usually have four transistors Q, Qxe2x80x2, Q0, Q0xe2x80x2 which are used to set up a current through a laser diode D. Then the light from the laser diode D hits a photo diode Dxe2x80x2 to produce an induced photo current through the photo diode Dxe2x80x2 and ensure the device under normal operation. Though a conventional circuit can drive the light-emitting element by a stably low operating voltage, it needs four transistors to compose the protection circuit. Hence its structure is more complex. Besides, the cost of transistors is more expensive than resistors. For the consideration of the reduction of cost and the simplification of space arrangement of circuits the applicant keeps on carving unflaggingly to develop xe2x80x9ca device having three transistors for driving a light-emitting elementxe2x80x9d through wholehearted experience and research.
It is an object of the present invention to provide a device having three transistors for driving a light-emitting element via a relatively low operating voltage.
It is another object of the present invention to provide a device with simpler circuit structures and less cost for driving a light-emitting element via a low operating voltage.
According to an aspect of the present invention, the device for driving a luminary via three transistors includes a driving circuit and a negative voltage circuit and a protection circuit. The driving circuit has a first transistor and a second transistor for producing a first signal. The negative voltage circuit is electrically connected to the driving circuit for transforming the first: signal into a second signal to be transmitted to the light-emitting elements thereby the light-emitting elements being driven in response to an operating voltage. The protection circuit includes a third transistor with an emitter and a base both connected to the light-emitting element and a collector connected to the base of the first transistor and the collector of the second transistor for controlling the operating voltage so as to stabilize an output of the light-emitting element.
Preferably, the light-emitting element includes a first diode and a second diode.
Preferably, the first diode is a laser diode and the second diode is a photo diode.
Preferably, the second signal is a negative voltage.
Preferably, the second signal is a direct current signal.
Preferably, the operating voltage is a sum of an absolute voltage of the second signal and a power voltage.
Preferably, the sum of an absolute voltage of the second signal and a power voltage is greater than an absolute voltage of the first signal.
Preferably, the operating voltage is ranged from 1 to 1.5 V.
Preferably, the driving circuit further includes an inductor and a first capacitor.
Preferably, the driving circuit is a first step-up circuit via capacitor-inductor oscillating.
Preferably, the first transistor is a NPN transistor and the second transistor is a PNP transistor.
Preferably, the third transistor is a bipolar transistor.
Preferably, the first signal is an alternating current signal.
Preferably, the negative voltage circuit is a negative multiple voltage circuit.
Preferably, the negative multiple voltage circuit includes a second capacitor, a third capacitor, a third diode and a forth diode. The second capacitor is electrically connected to the driving circuit. The third diode has an anode electrically connected to the second capacitor and a cathode grounded and the forth diode has a cathode electrically connected to the capacitor and an anode of the third diode and an anode. The third capacitor has one terminal electrically connected to the anode of the forth diode and the light-emitting element and another terminal thereof is grounded.
Preferably, the negative voltage circuit is a load voltage circuit and the driving circuit is a second step-up circuit via capacitor-inductor oscillating.
Preferably, the load voltage circuit includes a second capacitor electrically connected to the driving circuit and a third diode having an anode electrically connected to the second capacitor and a cathode grounded.
Preferably, the negative voltage circuit is a rectifier circuit.
Preferably, the rectifier circuit includes a third diode having a cathode electrically connected to the driving circuit and an anode and a second capacitor having one terminal electrically connected to the anode of the third diode and another terminal thereof is grounded.
In accordance with an aspect of the present invention, a device for driving a light-emitting element via three transistors includes a driving circuit, a negative voltage circuit and a protection circuit. The driving circuit has a first transistor and a second transistor for producing a first signal. The negative voltage circuit is electrically connected to the driving circuit for transforming the first signal into a second signal to be transmitted to the light-emitting element; thereby the light-emitting element being driven in response to an operating voltage. The protection circuit has a third transistor having a source and a gate both electrically connected to the light-emitting element and a drain electrically connected to a base of the first transistor and a collector of the second transistor for controlling the operating voltage so as to stabilize an output of the light-emitting element.
Preferably, the light-emitting element includes a first diode and a second diode.
Preferably, the first diode is a laser diode and the second diode is a photo diode.
Preferably, the first signal is an AC signal.
Preferably, the second signal is a negative voltage.
Preferably, the second signal is a DC signal.
Preferably, the operating voltage is a sum of an absolute voltage of the second signal and a power voltage.
Preferably, the operating voltage is ranged from 1 to 1.5 V.
Preferably, the sum of an absolute voltage of the second signal and a power voltage is greater than an absolute voltage of the first signal.
Preferably, the driving circuit further includes an inductor and a first capacitor.
Preferably, the driving circuit is a first step-up circuit via capacitor-inductor oscillating.
Preferably, the first transistor is a NPN transistor and the second transistor is a PNP transistor.
Preferably, the third transistor is a metal oxide semiconductor field effect transistor.
Preferably, the negative voltage circuit is a negative multiple voltage circuit.
Preferably, the negative multiple voltage circuit includes a second capacitor, a third diode, a forth diode and a third capacitor. The second capacitor is electrically connected to a driving circuit. The third diode has an anode electrically connected to the second capacitor and a cathode is grounded. The forth diode has a cathode electrically connected to the second capacitor and an anode of the third diode and an anode. The third capacitor has one terminal electrically connected to the anode of the forth diode and the light-emitting element and another terminal grounded.
Preferably, the negative voltage circuit is a load voltage circuit and the driving circuit is a second step-up circuit via capacitor-inductor oscillating.
Preferably, the load voltage circuit includes a second capacitor electrically connected to a driving circuit and a third diode having an anode electrically connected to the second capacitor and a cathode grounded.
Preferably, the negative voltage circuit is a rectifier circuit.
Preferably, the rectifier circuit includes a third diode having a cathode electrically connected to the driving circuit and an anode and a second capacitor having one terminal electrically connected to the anode of the third diode and another terminal grounded.
For understanding this application further, some figures and detail illustrations are shown as follows: